On the coexistence of ultra wideband systems with selected wireless systems

The distinct advantages of ultra wideband (UWB) technology have attracted great interest in recent years. Among the many applications of UWB technology, its promising capability for replacing wired connections by wireless means attracts much attention from the mass commercial market. However, its inherent ultra wide bandwidth nature has been seen as a threat for the existing and future wireless systems. The spectrum proposed for use by future UWB systems overlaps the frequency bands which are almost fully occupied by existing radio services for private or government sectors. This thesis presents the results of the coexistence studies between UWB and some selected wireless systems, i.e. terrestrial fixed microwave links, broadband radios in the public safety band, land mobile radios in the VHF/UHF bands and fixed satellite services in the C-band. According to their applications and operating locations, different scenarios and hence different propagation path-losses are modelled. As UWB devices will be mostly deployed in indoor environments, its propagation characteristics inside a typical residential flat are studied in more details. But in all practical cases, the four systems suffer from significant interference caused by single or multiple UWB transmitters. The link budget calculations show that the power spectral density limit of -41.3 dBm/MHz is not sufficient to protect these services if none of the interference mitigation measures are implemented. It is especially true for the mobile terminals which are usually operated in urban dense areas and with omni-directional antennas. Field measurements and analysis were also conducted to verify the theoretical model of the fixed satellite services. Further investigations into the mutual interference impacts between different UWB systems and a narrowband system using QPSK modulation as an example are performed by computer simulations in the radio frequency domain, based on the published UWB channel and system models. It is found that a direct sequence pulse amplitude modulated (DS-PAM) UWB system generally outperforms a time hopping pulse position modulated (TH-PPM) UWB system when it is functioning as either an interferer or victim. The effectiveness of spectral nulling interference mitigation technique by removing a sub-band is also investigated. An adaptive scaling factor for each sub-band is also introduced in order to optimize the interference mitigation and spectral efficiency.